Musculoskeletal System Chapter 19 Musculoskeletal System 1 Consists of Bones and Muscles Along with associated connective tissues Tendons, ligaments, cartilage Skeleton provides support to body and protection to vital organs Skull protects brain, rib cage protects heart and lungs Attachment of muscles to bones is responsible for movement of Body and its various parts The human skeleton is a unique variation on an ancient theme The human skeleton consists of An axial skeleton (skull, vertebrae, and ribs) An appendicular skeleton (shoulder girdle, upper limbs, pelvic girdle, and lower limbs) Bones of the Skeleton Functions of the skeleton Supports body Protects soft body parts Produces blood cells Stores mineral and fat Along with muscles, permits flexible body movement Bones of the Skeleton Classification of the Bones Axial Skeleton Midline of body Appendicular Skeleton Bones of limbs and the limb girdles Further Classified by Shape Long - bones of limbs Short - cube shaped bones of digits Flat - skull Irregular - like vertebrae and facial bones Round - like the patella All bones have depressions and protruberances (processes) for attachment of muscles, openings for nerves and/or blood vessels The Skeleton Skull: frontal bone temporal bone zygomatic bone maxilla mandible Pectoral girdle: clavicle scapula Thoracic cage: sternum ribs costal cartilages vertebral column Pelvic girdle: coxal bones sacrum coccyx femur patella fibula tibia tarsals metatarsals phalanges humerus ulna radius carpals metacarpals phalanges 1
hyaline cartilage (articular cartilage) growth plate (contains red bone marrow) compact bone medullary cavity (contains yellow bone marrow) periosteum blood vessel diaphysis Hyaline cartilage in lacuna concentric lamellae Compact bone Blood vessels osteon 100 m 50 m Osteocyte lacuna matrix cells in lacunae canaliculus s in lacunae nucleus 10/21/2011 Tissue organization in bones Bones are complex living organs Consisting of several kinds of moist living tissue Cartilage at the ends of bones Cushions the joints A sheet of fibrous connective tissue covers outer surface of bones Plays a role in bone repair in case of fracture Structure of long bones Illustrates tissue arrangement in a typical bone Compact bone is highly organized Composed of osteons tubular units Osteocytes (bone cells) lie in lacunae Arranged in concentric circles around a Central canals contain blood vessels, lymphatic vessels, and nerves Canaliculi connect lacunae with each other and the 19.1 Spongy bone has an unorganized appearance Osteocytes are found in trabeculae Numerous thin plates surrounded by unequal spaces Spaces filled with red bone marrow Red bone marrow produces blood cells In infants, red marrow is present in cavities of all bones More limited number of bones in adults hyaline cartilage (articular cartilage) (contains red bone marrow) compact bone medullary cavity (contains yellow bone marrow) periosteum blood vessel Diaphysis (Shaft) Anatomy of Bone Hyaline cartilage matrix cells in lacunae 50 µm Cartilage lacks blood vessels, thus slow to heal if injured (hyaline, bone): Ed Reschke; (): Biophoto Associates/Photo Researchers, Inc. 2
Compact bone osteon s in lacunae in lacuna concentric lamellae 100 µm Blood vessels osteon Osteocyte canaliculus lacuna nucleus Cartilage Not as strong as bone but more flexible Matrix is gel-like with many collagenous and elastic fibers No blood vessels (slow to heal) Three types of Cartilage Hyaline firm and somewhat flexible Ends of long bones, nose, ends of ribs, larynx, trachea Fibrocartilage - stronger, thick collagen fibers, can withstand both pressure and tension Intervertebral disks, knees Elastic - most flexible, elastin fibers Ear flaps and epiglottis Dense Fibrous Connective Tissue Rows of fibroblasts separated by bundles of collagen fibers Forms flared sides of the nose Ligaments - connect bone to bone Tendons - connect muscle to bone Bone Growth and Repair Remodeling of Bones Adult bone is continually broken down and built up Osteoclasts - break down bone matrix and release calcium to blood Osteoblasts - pick up calcium from blood and deposit it in new bone matrix Get trapped in matrix and become s within lacunae Remodeling can change bone thickness Affected by hormones and physical use 3
Bones of the Skeleton Joints Fibrous immovable Sutures between bones of skull Cartilaginous slightly movable Connected by hyaline cartilage Ribs / sternum Connected by fibrocartilage Intervertebral discs Synovial freely movable 19.2 Bones of the Skeleton Joints Synovial freely movable Bones are separated by a cavity Ligaments holds two bones in place form capsule Tendons help to stabilize the joint Synovial membrane produces synovial fluid Types of Synovial Joints Hinge joints permit movement in one direction only Ex: knee Pivot joint permit only rotational movement Ex: joint between radius and ulna Ball and socket joints permit movement in all planes Ex: hip joint Movable joints Provide the human skeleton with flexibility Strong fibrous connective tissues called Ligaments hold the bones together at joints Skeletal Muscles Head of humerus Humerus Scapula Ulna Ulna Radius 1 2 3 Ball-and-socket joint Hinge joint Pivot joint Skeletal muscle Skeletal Muscles Skeletal Muscles Skeletal Muscles Work in Pairs Skeletal muscles are voluntary Covered by layers of connective tissue called fascia Extend beyond muscle to form tendon Tendons attach skeletal muscles to bones Origin of a muscle is on the stationary bone Antagonistic pairs of muscles bring about movement in opposite directions triceps brachii ( r ela x ed) humerus tendons origin (contracted) insertion origin Insertion of a muscle is on the bone that moves triceps brachii ( relaxed) (cont racted) insertion radius tendons ulna 4
TEM 26,000 Mechanism of Muscle Fiber Contraction Muscle Muscles consist of several bundles of muscle fibers Each Muscle fiber bundle has several muscle fibers Muscle Fiber is a Muscle Cell Cosists of several Myofibrils (contractile portions) Myofibrils contain actin and myosin filaments s are units of contraction in myofibrils Glycogen for energy storage Myoglobin for oxygen storage s Are repeating groups of thick and thin filaments Are the contractile units Thick filaments (myosin) Thin filaments (actin) Bundle of muscle fibers Single muscle fiber (cell) Nuclei Myofibril Light Dark Light band band band Light Dark band Light band band A muscle contracts when thin filaments slide across thick filaments The sliding-filament model Explains muscle contraction Relaxed muscle Z Dark band Z The myosin heads of the thick filaments Bind ATP and extend to high-energy states The heads then attach to binding sites on the actin molecules And pull the thin filaments toward the center of the sarcomere Contracting muscle Fully contracted muscle Contracted sarcomere The mechanism of filament sliding Thick filament (myosin) Thin filament ATP Myosin (actin) head 1 ATP binds to a myosin head, which is released from an actin filament. ADP P 2 Hydrolysis of ATP extends the myosin head. ADP P 3 The myosin head attaches to an actin binding site. New position of ADP + P This sequence detach, extend, attach, pull occurs again and again in a contracting muscle. Though only one myosin head is shown in the figure, a typical thick filament has about 350 heads, each of which can bind and unbind to a thin filament about five times per second. They work together to generate muscle contraction Motor neurons stimulate muscle contraction Motor neurons carry action potentials That stimulate muscle contraction 4 The power stroke slides the actin (thin) filament toward the center of the sarcomere. 5
A motor unit consists of A neuron and the muscle fibers it controls Spinal cord Motor unit 1 Motor unit 2 The axon of a motor neuron Forms synapses with the muscle at a neuromuscular junction Motor neuron axon Action potential Mitochondrion Nerve Motor neuron cell body Motor neuron axon Neuromuscular junctions Muscle Tendon Muscle fibers (cells) Nuclei Tubule Endoplasmic reticulum (ER) Bone Myofibril Plasma membrane Ca 2+ released from ER Acetylcholine released at a neuromuscular junction triggers an action potential That passes along tubules into the center of the muscle cell Calcium released from the endoplasmic reticulum Initiates muscle contraction 6